This invention relates generally to galvanometer-type motors, and more particularly to a motor for driving an optical element to deflect at a high frequency or to otherwise modulate a beam of radiant energy impinging thereon.
Various forms of optical devices are in use which are adapted to scan, sweep, chop or to otherwise deflect or modulate a beam of radiant energy. Such optical devices are incorporated in mass spectrometers, bolometers, horizion sensors and in other instruments which utilize or analyze nuclear, X-ray or laser beams, or other beams of radiant energy in the visible, ultraviolet or infrared region of the spectrum. In recent years, the need has arisen for optical scanners adapted to sweep light beam across binary coded bars such as United Product Code symbols or similar indicia to carry out various computerized functions.
One known means for this purpose makes use of a galvanometer to deflect the optical element, the galvanometer being of the moving iron type in which a soft iron rotor or armature is biased by one or more stationary permanent magnets. The rotor is made to oscillate by supplying alternating current to at least one field coil included in the stator structure.
It is also known to make use of DC torque motors that include permanent magnet rotors and a sophisticated coil wiring arrangement to generate the required torque. The drawback of this type of motor is that the rotor possesses a relatively high mass and affords an unfavorable mass-to-torque ratio, making it virtually impossible to operate the motor at the high frequencies required in many optical scanning applications. Moreover, the complex coil arrangement dictated by these torque motors to generate the necessary torque introduces manufacturing difficulties and makes such motors expensive to produce.
In order to reduce the mass of the rotor in an optical scanner of the galvenometer type, U.S. Pat. No. 3,799,644 to Street and U.S. Pat. No. 3,549,800 to Baker both disclose galvanometer type motors in which a beam deflection mirror is mounted on a rotor which takes the form of a coreless coil rotatable within a permanent magnet stator. Not only are such motors magnetically inefficient, but the excitation current therefor must be delivered to the moving rotor coil, and to this end conductive torsion spring fibers are necessary. Such fibers are relatively delicate and adversely affect the operating life of the galvanometer.
Also of prior art interest are the patents to Montagu, U.S. Pat. No. 3,959,673 and 3,624,579 which disclose an optical scanning motor having a soft iron rotor mounted on a torsion spring between symmetrically-arranged stators having field windings. These stators are formed by two pairs of soft-iron pole pieces at diametrically opposed positions with respect to the rotor, a pair of permanent magnets cooperating with the pole pieces to define biasing and driving flux paths.
Of general background interest are the patents to Reich et al. U.S. Pat. No. 3,999,833; Carriker U.S. Pat. No. 3,900,749 and Kato et al. U.S. Pat. No. 3,874,778.